1. Field of the Invention
This invention relates to a vibration preventive rubber device for automobiles.
2. Description of the Prior Art
A tension rod which is a constructional member of a front suspension for automobiles has one end secured through a bracket to an automobile body side member and the other end secured to a transverse link of the front suspension. Between the tension rod and the bracket are sandwiched a vibration preventive rubber device comprising a pair of rubber bodies for the purpose of cushioning shocks and vibrations subjected to the automobile body and hence improving a comfortable ride ability of the automobile without degrading the steering ability and stability during driving of the automobile.
As such vibration preventive rubber device as shown in FIG. 2A, it has heretofore been proposed to provide a device comprising two cylindrical rubber bodies 7, 7' arranged in the front and in the rear of a bracket 5 and extended through by a tension rod 6, the two rubber bodies 7, 7' being sandwiched between washers 8, 8' and firmly secured to the bracket 5 by means of lock nuts 9, 9' threadedly engaged with the tension rod 6.
Such rubber bodies 7, 7' function to exhibit compression deformation only so that their spring constant slowly changes as a function of the amount of deflection as shown by a curve C in FIG. 5. The amount of deflection becomes excessively large when the load subjected to the rubber bodies 7, 7' exceeds a given value, thereby inducing a mutual interference between suspension links.
In order to eliminate such drawback, it has also been proposed to insert synthetic resin blocks A, A' into the rubber bodies 7, 7' as shown in FIG. 2B. Such conventional device has a deflection-load characteristic shown by a curve A in FIG. 5. As can be seen from the curve A, such conventional device suddenly changes its deflection at a point P, thereby inducing a premature damage failure at the boundary edge portion between the rubber bodies 7, 7' and the synthetic resin blocks A, A'.
In order to eliminate such disadvantage, it has further been proposed to provide a vibration preventive rubber device comprising a pair of hand drum-shaped rubber bodies 10, 10' sandwiched between washers 11, 11' as shown in FIG. 3. In such conventional device, if water, oil or the like is penetrated into a gap formed between the rubber bodies 10, 10' and the washers 11, 11', the frictional coefficient therebetween becomes remarkably decreased. As a result, as shown in FIG. 4, a pressure receiving surface 10a of the rubber bodies 10, 10' tends to easily slide over a supporting surface 11a of the washer 11 so that the pressure receiving surface 10a is not stopped by a flange 12 of the washer 11, but rides thereon. If the load subjected to the rubber bodies 10, 10' is increased, the pressure receiving surface 10a springs the flange 12 and hence is removed out of it, thereby losing the spring ability inherent to the vibration preventive rubber. In addition, the pressure receiving surface 10a of the rubber bodies 10, 10' is damaged by the flange 12 to induce a premature damage failure of the vibration preventive rubber device and degrade the durability thereof. Concerning its spring constant, the vibration preventive rubber device shown in FIG. 3 has a deflection-load characteristic shown by a curve D in FIG. 5. The curve D is of slowly rising up non-linear one so that it is impossible to exhibit an excellent stopper effect which is important for the automobiles.